As you drive west out of Miami along a road called Tamiami Trail, you come to a tract where you can feel the sprawl ending and the Everglades beginning. On your right, across the road from the last strip mall, is a large parcel of wetlands and pine trees protected by Miami-Dade County's Urban Development Boundary (UBD), a line drawn in the marsh to keep South Florida builders from encroaching any further on this unique ecosystem. Lowe's, the home improvement chain, wants to move the border so it can erect a new store on more than 20 acres of the wetlands; further south, developers want to hop the line to build a commercial park and thousands of new homes. Protesters, including Miami-Dade Mayor Carlos Alvarez, gathered to denounce the plans last week  but on Thursday the Miami-Dade County Commission approved the Lowe's and the office developments.

As they do in much of the Sun Belt, developers have always had the run of South Florida, which to many longtime residents has become Paradise Paved. And the 13-member Miami-Dade County Commission, as if imitating the Florida politicos of a Carl Hiaasen novel, has long been considered developers' most willing abettor. One of the Lowe's project's biggest backers on the commission is Jose "Pepe" Diaz, who is under federal investigation for allegedly receiving gifts from developers whose plans he'd voted for. (He denies any wrongdoing.) Another, Natacha Seijas, who at one commission meeting voiced her dislike of manatees, one of Florida's most beloved and endangered sea mammals, faced a recall vote in 2006 (which she defeated) due to public complaints that she also was too cozy with developers. Other commissioners face scrutiny for alleged conflicts of interest involving real estate sweetheart deals received from builders.

Commission critics say the measure to move Miami's UDB sends a troubling signal that could further dampen Washington's flagging enthusiasm for a $10 billion repair bill for the Everglades  the 18,000-square-mile "River of Grass" that is an American eco-treasure and an essential source of water and flood protection for Florida's burgeoning population. "We've essentially asked the country to support Everglades restoration," says Dawn Shirreffs, head of the South Florida development watchdog group Hold The Line. "Now the country will wonder just where our values really lie." Indeed, Floridians clamored for the joint state-federal restoration project when it began eight years ago. But the UDB dispute may indicate that they, like much of the rest of America, find it too hard to curb their insatiable development urges.

Diaz rejects the charge that the commission is in bed with builders. "All we're looking to do is find a balance between residential needs and environmental needs," he says. As for the wetlands Lowe's wants, Diaz insists, "It's muck, not pristine wetlands. " He adds that Lowe's has pledged to help build a new high school near the land. But state and county community planning agencies disagree with Diaz's assessment and have urged that the three development proposals involved in Miami's UDB clash be denied because, among other reasons, they would stretch water supplies and government services too thin. "Even if this wasn't about the environment, we still don't have the ability to provide the basic services as development keeps moving west" toward the Everglades, says Mayor Alvarez. He, like so many other U.S. mayors today, insists that the notion trumpeted by developers  that sprawl is an economic panacea that eventually pays for itself via new taxes, jobs and the like  is a delusion.

Alvarez says he'll veto the commission's vote; but commissioners may well override him. If so, it raises larger concerns about the Everglades and its stalled restoration effort. When it was announced in 1999, Washington seemed committed to the 20-year plan to fix a half-century's worth of draining, diversion and other damage that development had wreaked on one of the world's most delicate but vital ecosystems, and return it to something like its original state. But post-9/11, the Everglades fell down the priority list of the Bush Administration and Congress alike. Today the project is less than half finished, years behind schedule and billions of dollars over budget. Last year Congress had to override President Bush's veto of a $20 billion water preservation bill that included a sorely needed $2 billion for the Everglades.

Many Floridians fear local moves like letting Lowe's build beyond the UDB will also end up diminishing the urgency of the Everglades. "It would be highly hypocritical of us to be asking [Washington] for hundreds of millions of dollars for the restoration of the Everglades and then turn around and make decisions that infringe on the integrity of the Everglades," says Alvarez. "It shoots our credibility."

The developers haven't won just yet. Besides Alvarez's promised veto, state and county agencies have indicated they'll join Hold the Line and myriad other local civic groups to challenge the development proposals in court. One of their arguments: the Everglades isn't just a vital water source but an equally important buffer against flooding  the kind that could have alleviated the devastation Hurricane Katrina heaped on New Orleans had its own outlying wetlands not been so reduced. That is no small consideration in South Florida, as global warming is raising sea levels. "Any time you fill in wetlands you're creating impervious surfaces that exacerbate flooding," says Miami-Dade County Commissioner Katy Sorenson, one of four commissioners who opposed the proposals on Thursday. "Few cities are more impacted by this than Miami is."

But even if the builders prevail, they may find that astronomical gas prices and the abysmal real estate market will discourage future exurban development on Miami's western fringe. As Miami Herald columnist Fred Grimm put it this week: "Who the hell is going to buy a suburban house at the edge of nowhere with gas soaring beyond $4 a gallon?" That's the kind of economic muck that's hard to build on  and one that might end up holding the line for the Everglades.